Griffscobbie

I am trying to purchase a minibus in the uk to take to France. I have looked at which ones to take. The problem is: Most minibuses in the uk are one body size, so, if you want a factory fitted 9 seater Ford for example then you get a 9 seater but in the back there is space for 3 more seats. (great luggage area I thought). One of our Friends who lives in france says that this is not acceptable as it is classed as a 12 seater although it came out of the factory as 9. Can anyone assist with this matter!! Regards